7 Crucial Factors to Consider When Upgrading Your Home Heating and Cooling System During a Remodel
Most renovation budgets are dominated by line items that have little to do with how comfortable the finished home will be. The owners select tiles and cabinetry and defer hard decisions on heating and cooling to contractors who install "something comparable to what we had before." This is understandable, if misguided, given that furnaces and air conditioners comprise roughly 50% of the energy budget for the average American home, and major renovations occur once every two decades or so.
The following are things to think about while the walls are open, but before sheetrock is up and tacked to the studs.
1. Make sure the size of the new system is based on a load calculation (not the old one)
Upgrades to windows, insulation, and air sealing; additions or subtractions to the square footage; and other changes to the building envelope will have a significant impact on the heating and cooling needs of the remodeled home. A Manual J calculation considers all of these variables, along with solar gain, ceiling heights, ductwork location, and climate, and determines the appropriate size for the new system. Contractors who attempt to "eye-ball" the replacement based on the tonnage or BTUs of the old equipment are guessing. Oversized units cycle frequently and fail to dehumidify the space properly, while undersized units run constantly without ever catching up on extremely hot or cold days. Request a written load calculation from whomever you hire, and ask to see it before paying for anything. Contractors who can’t or won’t provide this information are best avoided.
2. Select a system type and fuel source prior to paint choices
This decision has ramifications for both the electrical and structural drawings, including the location and size of the fuel line or electrical service. Air-source heat pumps are increasingly standard equipment in cold climates due to recent improvements in inverter-driven compressors that allow for reliable operation well below freezing, and they offer the advantage of a single unit providing both heating and cooling functions. Zoning allows for greater flexibility in distribution, particularly in additions or bonus rooms where the ductwork cannot be easily extended, and ductless mini-splits can handle smaller jobs without disturbing the existing structure. Existing gas furnaces can be paired with a heat pump in a dual-fuel setup to take advantage of the lower operating costs of gas during peak heating periods.
Regardless of the type of system, keep in mind that the installation quality has a huge impact on the equipment’s ability to perform according to its rated specifications. Poor design and installation practices can cause the heat pump to grossly undershoot its published SEER2 and HSPF2 ratings, particularly if the line-set charge, airflow capacity, or commissioning protocol is incorrect. The same goes for furnaces, boilers, and all other heating equipment.
3. Re-engineer the ductwork while it is exposed
Long, meandering flex duct runs, undersized or altogether missing return ducts, and registers placed in inconvenient (or uninhabitable) locations all become fair game for modification when access is gained through open framing. Have the supply and return sizes evaluated in accordance with the new load calculation, and consider balancing the system with static pressure measurements if the current arrangement is incompatible with the new equipment. An improperly sized duct system will add noise, reduce capacity, and shorten the equipment’s lifespan, regardless of the quality of the components.
4. Design HVAC zones concurrently with the architectural layout
While single-temperature thermostats are perfectly adequate for most homes, large, open-plan renovations require a more involved approach. A sprawling family room with vaulted ceilings can be a problem for whole-house systems due to the sheer volume of air, while home offices tend to be far too warm due to their proximity to heating and cooling equipment. Finished additions on the second floor will also benefit from localized temperature control. Zoning uses dampers in the ductwork to segment the pressure and airflow distribution and can be far less expensive than installing multiple complete systems.
Zoning is best incorporated at the same time as the overall renovations, as the dampers need to be installed in accessible, conditioned locations, while the control wiring must be run before the ceiling drywall is reinstalled. Retrofitting a whole-house HVAC system with zoning capabilities can be prohibitively expensive due to the amount of drywall that must be removed.
5. Get the electrical system reviewed ahead of time
This is often an overlooked budget item that can come as a nasty surprise to homeowners who neglected to factor it in. Heat pumps, and particularly the electric resistance heaters that supplement them in colder climates, often draw far more current than the gas furnace and window AC combination they are replacing. If the service has already been maxed out to its rated capacity, a sub-panel or even a service upgrade might be necessary. The same goes for any additions to the overall square footage, which will require additional circuits to be brought in.
The line sets that carry the refrigerant between the indoor and outdoor units should also be considered when planning heat pump installation, particularly in terms of length and potential routing obstructions. Longer distances and more complex runs require larger diameter copper tubing and can add significantly to the cost of the equipment. Consider the placement of the condensing unit in relation to the new interior finishes; what seemed like a convenient location for it may turn out to be a 40-foot run of refrigerant line once the renovations are complete. The final location of the condensing unit and its access path to the building’s perimeter should always be finalized before the framing and drywall work begins, lest the extra line sets and fittings add an unplanned $1,000+ to the final bill.
Gravity drainage for the condensate lines requires slope, which necessitates planning ahead if the new HVAC equipment location does not provide a natural downward slope. If the unit is installed in a low spot or an otherwise inaccessible area, a condensate pump will be required to remove the standing water produced by the air conditioning system. Either solution should be factored into the framing plans to avoid unpleasant surprises later in the process.
6. Don’t forget to account for fresh air exchanges in the insulation and air-sealing budget
New insulation and air sealing materials often make the building envelope substantially tighter than it was before the renovations began. While this is generally desirable, it also limits the amount of passive ventilation available to the home, which impacts indoor air quality. An Energy Recovery Ventilator or Heat Recovery Ventilator is an excellent addition to any home with substantial air sealing, as it actively moves and filters outside air while recovering up to 90%+ of the energy from the stale air being expelled. It’s an ideal complement to the new HVAC system, particularly when paired with an appropriately sized MERV filter and humidity control.
Without some sort of mechanical ventilation system, the renovated home can actually be less healthy than the one it replaced.
7. Specify the sequence and efficiency requirements in advance
Make sure the mechanical rough-in occurs before the drywall install commences. It seems obvious, but the last thing anyone wants is to have the refrigerant lines and ductwork fished through unfinished stud cavities in order to meet a deadline. The alternative is having the electrical contractor fish the thermostat wire through the insulated walls, or having the sheetrockers contaminate new HVAC equipment with their drywall dust. The installation of heating and cooling systems should always take place while the framing bays are still open and accessible in order to avoid these situations.
When reviewing contractor bids, specify exact efficiency standards in terms of SEER2 and HSPF2 ratings, and ask if the proposed equipment is variable-speed or single-stage. Request a copy of the load calculation to be reviewed as part of the agreement signing process, and remind the contractors that permits are a necessary expense. Permits tied to mechanical rough-ins and inspections are crucial for verifying that everything was installed according to code, protecting both the warranty and the resale value of the home. Meanwhile, rushing the process in order to save money can end up costing far more in both time and money if an inspector or a future buyer notices discrepancies during the final walkthrough.
Remember that permits, new thermostat wire, condensate pumps, outdoor unit reinforcements, and additional ductwork insulation are all expenses that factor into the final cost of a renovation. They may not seem like much on their own, but combined with one another they can add up to a substantial increase to the initial quote if they are not accounted for.
Run the numbers on rebates and tax credits before specifying equipment
High-efficiency HVAC equipment typically carries a higher sticker price, but the 25C tax credit reduces the effective cost by up to 25%, with many utility companies offering additional incentives on top of that. Pair this with the energy savings from the new equipment and the rebates that may be available for replacing old, inefficient systems, and the break-even point for the upgraded equipment may be far closer than expected. These figures should be used to inform the equipment selection rather than the other way around.
During a renovation, the home gets one shot at the comfort systems, which is why it’s so important to maximize the value of that opportunity. The home’s load calculation, system type, ductwork design, and utility requirements must all be reviewed at the same time the renovation plans are being finalized. With the fundamentals in place, the owners can focus on the cosmetic aspects of their remodeling project with confidence that their investment will be worth the time and money it takes to finish the job.